A large number of boom lifts, utility cranes, light turning devices and medium duty cranes are used for construction and maintenance tasks. Most of these devices consist of a wheeled vehicle or platform upon which a rotatable body is mounted. In most of these devices the rotation is performed by a worm gear driven slewing bearing.
In all the current worm gear driven slewing bearings the worm gear is mounted on an open housing and then mounted to a slewing bearing with several fasteners to allow the adjustment of the backlash. Both the worm gear and the gear teeth of the bearing are exposed and visible. They are lubricated with grease but the grease does not remain between them because of the friction between them. Consequently the worm gear and the gear teeth of the bearing quickly run dry. Further, these boom lifts are used under adverse conditions and because these parts are exposed to the elements such as water, dust and dirt the wear is increased tremendously.
Because of the lack of grease when rotating the unit, a condition know as slip stick occurs. The amount of torque necessary to turn the unit increases tremendously and the rotational speed is decreased and then suddenly the friction is overcome and less torque is necessary and the rotational speed is increased. This causes difficulty for the operator of the boom in positioning it.
In this invention the worm gear and the teeth of the bearing are totally enclosed from the outside elements so no dirt, dust, water or particles can get between them. Further, they are continuously and completely lubricated by an oil bath. Thus the need to grease is eliminated and the occurrence of slip stick is eliminated because the worm and gear constantly have an oil film between them. This reduces the wear and resultant backlash between the worm and the gear. A little backlash is multiplied many times over at the end of the boom making the operation of the boom difficult.